This invention relates to image data conversion devices, and more particularly to an image data conversion device which carries out a conversion process for the formation of images, such as changing the arrangement of picture element data or partially extracting picture element data.
One example of a conventional image data transmission device, as shown in FIG. 4, comprises: a central processing unit 1 including for instance a micro-computer: a tri-state buffer circuit 2 connected between the input/output port of the central processing unit 1 and a bus line 3, the circuit 2 being made conductive or non-conductive in response to a control signal CS from the central processing unit 1; a memory unit 4 connected to the bus line 3 and having a RAM (random access memory); and an interface circuit 5 interposed between the bus line 3 and an external device such as a monitor television set. The interface circuit 5 applies a request signal REQ to the central processing unit 1 when required.
The above-described image data transmission device is based on a so-called "DMA (direct memory access) transmission system". When, as shown in part (a) of FIG. 4, a signal REQ requesting the tri-state buffer circuit 2 to be made conductive is applied to the central processing unit 1 by the interface circuit 5, the control signal CS is supplied to the tri-state buffer circuit 2 by the central processing unit 1 so as to make the tri-state buffer circuit 2 conductive, thus permitting data transmission between the central processing unit 1 and the interface circuit 5 and the memory unit 4. On the other hand, when, as shown in part (b) of FIG. 4, a so-called "DMA request" is made to the central processing unit 1 with the aid of a request signal REQ, the control signal CS is applied to the tri-state buffer circuit 2 by the central processing unit 1 so that the tri-state buffer circuit 2 is rendered non-conductive (or high in impedance), thus inhibiting data transmission between the central processing unit 1 and the interface circuit 5 and the memory unit 4. Upon the DMA grant, data can be transmitted directly between the interface circuit 5 and the memory unit 4, and therefore an external device (not shown) can access the memory unit 4 through the interface circuit 5 for transmission of data.
Thus, in the transmission of data, it is unnecessary for the external device to use the central processing unit 1. This means that the time required for the transmission of data is greatly reduced. The system is considerably effective in an image reproducing apparatus in which image data stored in a memory unit (4) are transmitted to an external device such as a monitor television set.
However, the above-described image data transmission device is still disadvantageous in the following points: In the conventional image data transmission device, the image data are sequentially transmitted while in the memory unit the address regions are renewed one after another in one or the opposite direction. Therefore, the device cannot meet the requirement that the image data be changed in arrangement or partially extracted to quickly reproduce a modified image as required. That is, the DMA transmission system can transmit image data at high speed, but cannot change the arrangement of image data. If it is required to change the arrangement of image data according to the DMA transmission system, it is necessary to process the data under program control of a central processing unit such as a micro-computer, and therefore the data processing speed will be considerably low.